The present invention generally relates to fiber optic systems and, more particularly, to a method of making a hollow polymeric light conductor by coextrusion.
Fiber optics have revolutionized the communications field and are finding many applications in the medical field. Fiber optics are also proving useful in areas as diverse as computer systems, automotive systems, aerospace systems, and advertising signs. Thus, there is an ever-present need for refining and improving upon fiber optic systems for use in a wide range of industries. In this regard, the following patent applications of the assignee are hereby incorporated by reference: Larry J. Laursen, et. al., U.S. patent application Ser. No. 003,774, entitled "A Method Of Making A Polymeric Optical Waveguide By Coextrusion", filed on even date herewith; Theodore L. Parker, et. al., U.S. patent application Ser. No. 088,083, entitled "Polymeric Optical Fiber", filed Jan. 21, 1987, now abandoned, in favor of Ser. No. 014,997, filed on Oct. 8, 1987 herewith; and Theodore L. Parker, et. al., U.S. patent application Ser No. 831,775, entitled "Polymeric Optical Fiber", filed on Feb. 20, 1986.
A variety of translucent/transparent materials, such as glass and amorphous polymers, have been utilized as light-conducting fibers in fiber optic systems. However, polymers offer several advantages over other fiber optic materials for applications where a small degree of signal loss is acceptable. For example, plastics have a higher numerical aperture than glass. Additionally, polymer fibers are relatively inexpensive and lightweight. They are also flexible and resistant to breakage, thereby facilitating assembly and installation. Other advantages include the fibers' immunity to electromagnetic interference. This is particularly important in automotive applications, where sophisticated multiplex data systems are subjected to electromagnetic interference generated by the alternator and spark plugs.
Light-conducting fibers in fiber optic systems are generally encased in a sheath or cladding of material having a lower index of refraction than the conducting fibers. Proper indices of refraction of the conducting material and cladding are necessary to provide a high degree of internal reflection of light traveling down the fiber and to provide an appropriate numerical aperture for the transmitting system. The greater the difference in refractive indices, the greater the numerical aperture and, thus, the more light will be trapped and transmitted through the optical waveguide. Accordingly, the lower index of refraction of the cladding relative to that of the core material enables the cladding layer to reflect light inwardly toward the core as the light travels down through the conducting core. While air has a lower index of refraction (i.e., 1.0) than any plastic material that could be used for the cladding, the plastic cladding protects the surface of the core from dust, dirt, and scratching. Thus, a plastic cladding is desirable since it can provide a smooth and continuous interface at the surface of the core, and thereby minimize the dispersion of light into the surrounding environment.
Fiber optic assemblies are particularly useful in examination devices involving imaging. For example, fiber optic assemblies are highly useful in medical probes such as laryngoscopes, bronchoscopes and intravenous or intracardiac examining devices. They can also be advantageous in optical examining devices such as borescopes. Such fiber optic assemblies have generally included a first bundle of fibers for imaging purposes and a second bundle of fibers for transmitting light to the end of the assembly. In such an assembly, the light transmitting fibers are generally disposed around the image forming bundle to both guide the image forming bundles and illuminate the target area for imaging. Such assemblies are typically made with glass fibers in a hand lay-up procedure, and are therefore quite expensive. This operation is not only laborious and delicate, but the resulting conductor has reduced efficiency because a significant portion of the area occupied by the light transmitting bundle is not conductive due to the gaps between the individual glass fibers.
One attempt at forming a continuous light conducting ring involved the drilling of a solid polystyrene core and depositing a layer of polymethyl methacrylate (PMMA) on either side of the core. However, problems encountered using this method included difficulties in maintaining the dimensions and physical properties of the conductor, and an inability to obtain good smooth surfaces between the cladding and conducting layers. Uniform dimensions and physical properties and smooth interfaces are desirable to reduce light dispersion and increase light transmission.
Thus, it would be desirable to provide a continuous annular light conductor with uniform dimensions and physical properties to ensure minimal dispersion of light and a high degree of light transmission.
It would also be desirable to provide a hollow light conductor with smooth surfaces between the cladding and core conducting layers to further enhance light transmission.
It would further be desirable to provide a hollow light conductor with a continuous annular core for maximizing light conductivity.
It would also be highly desirable to provide a continuous high-speed and, therefore, low cost method and apparatus for manufacturing hollow light conductors with the above properties which ensure the minimal dispersion of light and a high degree of light transmission by the light conductor.
It would further be desirable to provide a method of making a hollow light conductor which has a very small diameter and wall thickness.